Manila: The International Criminal Court (ICC) has told the Philippines that it has begun a preliminary examination of a complaint accusing President Rodrigo Duterte of crimes against humanity, his spokesman said on Thursday.

The complaint, which says Duterte is complicit in the illegal deaths of thousands of Filipinos during his war on drugs, was "a waste of the court's time and resources" and the examination would be the end of the process, presidential spokesman Harry Roque said.

About 4,000 mostly urban poor Filipinos have been killed by police in the past 19 months in a brutal crackdown that has alarmed the international community. Activists believe the death toll is far higher.

Roque said he had discussed the ICC issue for two hours the previous night with Duterte, a former prosecutor, adding that the president more than willing to face trial.

"He's sick and tried of being accused," said Roque, an international law expert.

"He wants to be in court and put the prosecutor on the stand."

The website of the ICC, which sits in the Hague in the Netherlands, carried no new information concerning the complaint against Duterte. The court's office could not immediately be reached for comment.

Since it was set up in 2002, the ICC has received more than 12,000 such complaints or communications, just nine of which have gone to trial.

Prepared to go to prison

Duterte has dared it to bring him to trial and said he would rot in jail to save Filipinos from crime and drugs.

His tirades against the court are notorious, and include calling it "bullshit", "hypocritical" and "useless", stemming from one of its prosecutors saying there could be grounds for an investigation into his bloody crackdown.

He also threatened to cancel the Philippines' ICC membership and said European lawyers were "rotten", "stupid", and had a "brain like a pea".

Police say those thousands of killings were during legitimate anti-drugs operations in which the suspects had violently resisted arrest. Duterte has boasted about killing thousands of drug dealers and has told police they can kill if they believe their lives are in danger.

But his critics accuse him of incitement to murder and of refusing to properly investigate allegations that police are planting evidence, fabricating reports and executing users and dealers.

Duterte rejects such accusations and typically chides the international community for listening to what his government says are biased human rights groups that have no proof.

A Philippine lawyer filed the initial ICC complaint against Duterte and at least 11 senior officials last April, saying crimes against humanity were committed "repeatedly, unchangingly and continuously" and killing drug suspects and other criminals had become "best practice".

Senator Antonio Trillanes and Congressman Gary Alejano sent a supplementary communication several months later urging an ICC investigation, which included a list of public statements made by Duterte that they said amounted to 'shoot-to-kill' orders.

Trillanes said the examination "should jolt Duterte into realising that he is not above the law".

Roque called the complainants "domestic enemies of the state" and said the ICC had no jurisdiction.

Pending court cases meant domestic legal processes had yet to be exhausted, and the anti-drugs campaign was a sovereign issue, he said.